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Advanced Protection Technologies Surge Protection Overview Prepared by: Lou Farquhar, PE, CEM, GBE VP – APT Engineering Service (800) 237-4567.

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Presentation on theme: "Advanced Protection Technologies Surge Protection Overview Prepared by: Lou Farquhar, PE, CEM, GBE VP – APT Engineering Service (800) 237-4567."— Presentation transcript:

1 Advanced Protection Technologies Surge Protection Overview Prepared by: Lou Farquhar, PE, CEM, GBE VP – APT Engineering Service (800) 237-4567

2 Copyright APT 2012 2 APT 26 Years Supplying Surge Protective Devices ISO 9001-2008 Quality Management System ISO 17025 evaluation by UL Power Quality Assurance magazine – PQ 50 Company Frost & Sullivan ranked APT – Leading Supplier of Three Phase Devices Market Engineering Customer Focus Awards Members of UL, IEEE, NEMA standards committees

3 Copyright APT 2012 3 What Is a Surge/Transient? High amplitude, short duration overvoltage Can be positive or negative polarity Tidbit: Transient: > two times system’s RMS voltage Noise: < two times system’s RMS voltage Transient Overvoltage – Can be thousands of volts Millionths of second

4 Copyright APT 2012 4 What Causes Surges/Transients? Lightning Switching: – Load Switching – utility & customer Motors, Large Loads, Faults, Fuse Operation – Source Switching Smart Grid, Gensets, PV, Wind Turbine Internally generated surges: ≈70% Externally generated surges: ≈30% In outdoor environment, this ratio probably reverses

5 Copyright APT 2012 Effects of Transient Voltages? Microelectronics Intolerant to Surges Disruption – Lockups, Downtime & Interruption costs – Computing glitches and errors Degradation – Microelectronics – Slow & continuous damage to motor insulation Destruction – Failed microelectronics, ballasts, motors, controllers, etc. Maybe analogous to: - ‘Water hammer’ in a plumbing system - ‘Rust’ to microelectronics

6 Copyright APT 2012 MOV - Metal Oxide Varistor Varistor - variable resistor Semiconductor; generally zinc oxide Connects parallel to load (not series) Thickness determines clamping voltage Diameter determines current capacity MOV symbol

7 Copyright APT 2012 7 MOV - Metal Oxide Varistor Normal voltage Overvoltage I = V 120V R 10 9  = 0.12  A I = V 6000V R 1  = 6000A MOV seeks to equalize overvoltage Voltage sensitive conductor: V = IR & I = V/R At ‘low’ voltages: very high impedance,  10 9  : I  0A Above ‘threshold’ voltage: resistance approaches 0  : I = high A – Current diverts through MOV as I = V/R (high V, low R) Trivial leakage current Surge Current

8 Copyright APT 2012 8 MOV - Metal Oxide Varistor Overvoltage diverts through MOV as current Voltage is “clamped” or “equalized” as energy is transferred to other side of MOV(s) MOV does not ‘absorb’ surge, however, I 2 R heat is retained Bidirectional – Operates same for positive or negative surges Creates a momentary low impedance (acting like short-circuit) to pass transient energy to earth; analogous to water heater pressure relief valve + - + -

9 Copyright APT 2012 9 SPD Operation MOV/SPD Acts as a momentary ‘short circuit’ ‘short circuit’ ≈ no overvoltage ≈ protected load Load 1 Load 2 Load 3 Layman’s Terms: Visualize an ‘electronic guillotine’ that chops the head off a surge and sends it away After the surge, MOV/SPD automatically resets itself to high impedance state drawing no current

10 Copyright APT 2012 10 SPD Operation Load 1 Load 2 Load 3 MOV/SPD Acts as a momentary ‘short circuit’, then resets itself after the surge ‘short circuit’ ≈ no overvoltage ≈ protected load

11 Copyright APT 2012 11 SPD Connector Leads Need short lead lengths! NEC 285.12: “The conductors used to connect the SPD (surge arrester or TVSS) to the line or bus and to ground shall not be any longer than necessary and shall avoid unnecessary bends” Industry typically states: Each foot of conductor adds  100 - 170V to clamping voltage No Sharp bends or kinks No Wire Nuts! Right Hand Rule – can cancel inductive effects by bundling, tie-wrapping conductors together

12 Copyright APT 2012 12 2008 NEC Art 285

13 Copyright APT 2012 13 2011 NEC Art 285

14 Copyright APT 2012 14 APT Here to Help: (800) 237-4567 Specification Assistance Training Sounding Board for issues Competitive crosses or analysis General Help On-Line webinar services Forensic Testing & Analysis of failed SPDs Etc.


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